Good to see you back here, Penny.
I've done a lot of down projects, and they've always been a bit messy, but here is how I do it:
I empty some down into a paper grocery bag. Then I use a shop vacuum with the tube attachment to vacuum up the down. I tape a circle of no-see-um netting over the hose, then attach the tube and turn it on. Then, holding my hand over the open end, I disconnect the tube, slide it into the baffle I'm filling, and blow the down into the baffle.
A bit unscientific, I know, but for big projects (like a quilt) I pre-weigh the down on a digital scale so I have a general idea of how much I'm adding to each baffle. And no matter what you are going to lose some down. I work in the garage to contain the mess; some folks here work in a tent, but I don't like the idea of breathing down "snow flakes" in such an enclosed space. Figure from 5% to 10% loss.
One thing I've learned is every down supplier I've used tends to somewhat overstate the fill power of their down -- in my experience an ounce of "800 fill" down will, in practice, expand to fill about 700 to 750 cubic inches of space, so I always buy 20% extra to account for that and for lost down.
Hope this helps and I hope I've explained it in a manner that isn't too confusing.
My blog on politics, the environment and the outdoors: Haiwee.blogspot.com